Satin white-clay compositions and methods of manufacture

ABSTRACT

A method of making a paper coating pigment by forming a satin white in aqueous suspension, adding thereto a kaolinite and removing a major portion of the water from the aqueous suspension to form a free flowing powder.

United States Patent [191 Conley et a1.

[ Dec. 17, 1974 SATIN WHITE-CLAY COMPOSITIONS AND METHODS OF MANUFACTUREInventors: Robert F. Conley, Elizabeth, N.J.;

Billy Reid Catherwood, Macon, 021.; Mary Kate Lloyd, Elizabeth, NJ.

Georgia Kaolin Company, Elizabeth, NJ.

Filed: Apr. 17, 1968 Appl. No.: 721,955

Assignee:

US. Cl. 106/214, 106/288 B, 106/306, 106/308 C, 117/156 Int. Cl C08b27/02 Field of Search 106/214, 309, 306, 288 I, 106/308 C; 117/156References Cited UNITED STATES PATENTS 2/1922 Ryan 106/214 2,034,5193/1936 Larson 106/306 2,435,600 2/1948 Rafton 3,372,043 3/1968 Fanselow106/309 X Primary ExaminerLorenzo B. Hayes Attorney, Agent, orFirmBue1l, Blenko and Ziesenheim 5 7 ABSTRACT A method of making a papercoating pigment by forming a satin white in aqueous suspension, addingthereto a kaolinite and removing a major portion of the water from theaqueous suspension to form a free flowing powder.

9 Claims, 3 Drawing Figures 10 RPM Brookfield Viscosity, cp.

IOOO

0.15% D equesf 0.15% (wupog 20% Dequest 0.20% (MP0 1 70% Kaolinife 30/Satin White 456 8 lO 15 2O PATENTU, SE81 71974 Fig.l.

Fig.2.

Fig.3.

I0 RPM Brookfield Viscosity, on

ID RPM Brookfield Viscosity, cp. lO RPM Brookfield Viscosity, cp.

0.4% TSPP 3000 O 0.133 M1 00 0 +0.267"/ (NuPO 2000 0.4 /o NH 0H 36 0.4%Dequasl |000- 70%, Kaolinlte 30% Sulln White I l l II l 2 3 4 5 6 a :0I5 20 Days 5000 70% Kcolinlle 0% Satin White 0.4% (NuPO l I l l l I II 23 4 5 e 8 l0 I5 20 Days 0/o Kaolinile 30%; Sulin White 0% Daquosl 0.20%(NuPO l INVENTORS Roberl F. Conley, Billy Reid Colherwood and Mary KateLloyd BIO l5 20-- This invention relates to satin white-claycompositions and to improvements in optical properties of coated paperby application of specific satin white-clay compositions thereto. Morespecifically, this invention relates to the processing of improved satinwhite-clay pigments used in the coating of paper and to an improvedcoating pigment.

ln the commercial operation of coating paper, dispersions of kaoliniteand adhesive, along with other pigments usually of high refractiveindex, are roll or blade coated onto a moving paper sheet and driedthereon. It has been observed that the presence of micro-voids in thedried coating improve certain optical properties, notably opacity andgloss, and to a lesser extent brightness and whiteness. One mode ofintroduction of controlled voids is by the use of certain acicularpigments in small concentrations. it has been theorized that suchpigments take up space by brush'pile" configuration and slowly releasewater during the drying process and thus introduce voids of a sizerelated to the particle length.

One such material is known in the trade as Satin White," a calciumsulfo-aluminate of somewhat indefinite composition, but believed to beprimarily 3 Ca0- .Al O .3 CaSO .32 H O. Satin White, as now known in thetrade, is produced by mixing a solution of calcium hydroxide with one ofaluminum sulfate in stoichiometric proportions. The chief problem in themanufacture of satin white is stability it must be kept in watersuspension, usually at about 20-25 percent solids. lt is well recognizedthat drying satin white destroys it together with the useful opticalproperties it imparts. It is observed that the suspension is evendegraded at temperatures above 75 C. While 75-80 percent water may behigher than necessary for its stability, the extremely thixotropicviscosity of satin white in water makes it completely impractical tohandle at solids higher than 25 percent. The high water contentintroduces several commerical problems. Shipping costs are exorbitantand shipping is prohibited where exposure to cold weather results. Thelatter problem arises because EXAMPLE 1 A satin white composition isformulated by slurrying 5 parts of high purity lime in parts water atroom temperature and thoroughly mixing. A second solution of 25 percentaluminum sulfate is made up, a volume corresponding to about a Al (SO 18H O Ca(OH) weight ration of 1.50. The aluminum sulfate solution is addedslowly (about 30 minutes total) to the lime solution, so the temperatureof the mixture does not rise above about 32 C. The precipitation iscontinued until a pH of 1 1.9 is reached. Thereafter a starch suspensionis added in an amount corresponding to 10 percent by weight of theprecipitated calcium alumino-sulfate, or about 1.35 parts dry starchbased on lime formulation. Starch acts as a binder in the finishedcoating formulation-and its addition to satin white improves therheology somewhat.

The precipitate is filtered under pressure to attain 20-25 percentsolids.

EXAMPLE 2 A commercial coating grade kaolinite which had been previouslyacid flocced, filtered, and dried (median particle size 0.7;; percent2p.) was formulated at about 50 percent solids in water withoutdispersant.

EXAMPLE 3 To this suspension of clay from Example 2 was added the satinwhite of Example 1 in a proportion corresponding to 70 parts drykaolinite and 30 parts dry satin white. The composite material was about30 percent solids. The slurry was divided into three parts.

Part A was dried as formulated in an oven at 50 C. overnight.

Part B was vacuum filtered and oven dried at 50 C. overnight.

Part C was spray dried in a Nichols Niro Utility spray dryer having aninlet gas temperature of 380 C. and an outlet gas temperature of 135 C.While this temperature is much higher than the oven drying temperature,the contact time is only a few seconds.

Properties of the various mixtures and components in Example 3 are givenin Table I.

TABLE I Formulated Brookfield Viscosity, c.p. Sample Solids, 10 RPM RPMSatin White 23 (max) 8,400 1,400 Kaolinite Clay 54 (max) 288 67 (A) 70%K-30% SW. 39 l0,000* (B) do. 39 l0,000* (C) do. 39 3,680 476 (D) do.fresh 40 1 1,200 2,140

' Oven dried samples could not be fully redispersed due to the presenceof cemented aggregates.

It is apparent that Sample C is better, with respect to 0 rheology, thanB or A, and even better than a freshly formulated composite. Sample C isa free flowing, dryappearing powder containing about 5.0 percentmoisture. All spray dried materials referred to later made by thisgeneral process contain 5 percent or less moisture and are also freeflowing powders which show no degradation after several weeks aging.

The samples in Table 1, except for A and B, were formulated intostandardized coating compositions and TABLE II (a) Optical Properties ofUncalendered Sheets commercial processing. In spray drying a slurry ispumped through fine nozzles and atomized in a hot air stream. A lowviscosity and high solids are absolutely Coating whiteness Weight GlossBri mess Index, Opacity, Sample lb./ream at 75 at 4 my,

Satin White 5 2.4 71.7 26.7 93.3 Kaolinite Cla 5 4.6 73.2 26.9 93.7 (C)70% K-3 SW. 4.5 3.0 75.3 22.3 95.5 (D) 70% K-30% S.W. fresh 4.5 2.0 72.826.8 94.0

Reflectance difference, 700 mp- 400 my. 2 Reflectance difference at 530mp. over white/black The optical properties of Sample C are noticeablybetter than a freshly formulated equivalent mixture. (Note: While anincrease in value in most columns signifies an improvement, a low valuefor whiteness index is indicative of quality. A difference of 1 percentin any of the optical properties is significant in optical character.)While gloss is better on the straight satin white, such a formulation isnot practical from its rheological, printing, drying, and accessoryoptical properties.

EXAMPLE 4 essential for economic operation of such dryers. Also, /incommercial operation it is not always feasible to spray dry a slurryimmediately upon its formulation. It

Samples of 70-30 blends respectively of kaolinite and satin white wereformulated similarly to Example 3 with varying dispersants. Stabilitytests were performed using viscosity measurements as a criterion. Theresults are illustrated in the accompanying drawings in which: FIG. 1 isa graph of aging characteristics of 25 percent solid suspension usingvarious dispersants;

FIG. 2 is a graph as in FIG. 1 using various concentrais common practiceto integrate many production batches into a holding tank to minimizeinconsistencies and to balance out equipment throughput rates.Consequently, the rheological stability of a slurry is of considerableimportance.

EXAMPLE 5 Samples similarin composition and formulation as set forth inExample 4 were dried on the commercial spray dryer to evaluate theeffect of the initial dispersant and spray drying on finished coatingproperties. Preparation was similar to Sample C except a minimumdispersant level was employed to achieve pumping requirements for thespray dryer. Coated sheets were prepared with a slight starchmodification of those in Example 3. The results appear in Table III.

TABLE III (a) Physical Properties of Predispersed & Spray DriedFormulations of finished coating formulation tions of sodiumhexametaphosphate; and

FIG. 3 is a graph as in FIG. 1 using various concentrations of sodiumhexametaphosphate and Dequest.

The composites predispersed with mixtures of sodium hexametaphosphateand organic. phosphonates such as Dequest." (Dequest" is the trade markof Monsanto Chemical Company for its brand of amino tri(methylphosphonic acid) and the salts thereof) show the lowest initialviscosities and maintain a low level for an extended period. Suchproperties are essential for TABLE [II (b) Optical Properties of CoatedSheets after Calendering* Coating Gloss Brightness Sam- Weight at atwhiteness Opacity, ple lbJream 457 mp, Index,

(E) 5 [1.6 73.3 36.4 90.0 (F) 5 15.0 74.8 32.6 90.5 (G) 4.5 12.2 73.934.9 89.9 (H) 5.5 17.0 75.2 32.3 9L4 T BL III k oatt ied OpticalProperties of Coated Sheets after Culendering* 2 nips at 5 psig Acomparison of physical properties in Table III (a) shows that thepredispersion, while reducing viscosity for the spray-dryer feed(FIG. 1) results in a slight increase in finished formulation (coatingcolor) viscosity. While any viscosity increase is counter to goodcoating practice, this amount is not beyond the compensation capacity ofcommercial coating machines. Of even greater importance is the viscositycomparison of samples F, G, and 1-1 with D, a formulation whoseviscosity is impractically high.

The optical properties in Table 111 (b) show an even greater advantageof predispersion in the spray drying operation. All predispersed samplesare better than the straight spray dried member (in both compositeratios) in almost all optical properties.

EXAMPLE 6 TABLE IV (a) Optical Properties of Uncalendered Sheets TABLEIV (b) Continued 0mm PROPERI'IES (F COATED SHEES m CPLENDERINGH GlossBrightness Whiteness Opacity,

Sample at at 457 mu, Index,

(O) 14.0 75.0 32.0 91.0 (P; 18.3 75.1 31.5 91.2 (Q 16.0 74.1 33.6 91.0R) 16.7 74.5 33.2 90.1 S) 16.8 74.1 33.3 91.0 19.6 75.0 31.0 91.9

* 2 nips at 5 psig which after drying may subsequently be made up intoaqueous coating compositions the steps of:

a. forming a satin white composition in aqueous suspension;

b. adding a kaolinite to said aqueous suspension of satin white insufficient amount to retain the effectiveness of satin white as a papercoating pigment on rewetting after drying; and

c. removing water from the aqueous suspension to form a free flowingpowder.

2. The method as claimed in claim 1 wherein the kaolinite is added as anaqueous suspension.

3. The method as claimed in claim 1 wherein a paper coatingadhesivestarch is added to said admixture prior Coatin Weight Bri tnessWhiteness Sample Dispersant lb/ream at 4 ma, Index, Opacity,

(M) Satin White 6 75.4 30.8 90.5 (N) Kaolinite 6 74.1 34.4 91.1 (0) 70%K-30% S. W 2 none 6 75.7 30.9 91.2 (P) 70% K-30% SW. 0.2% Dequest 0.2%(NaPOflB 6 76.2 29.6 91.9 (0) 70% K-30% SW. 0.3% N OH 6 75.5 31.2 91.5(R) 70% K-30% s.w. 0.3% Nau 2 1 6 75.2 31.6 90.8 (S) K-20% S.W none 675.4 31.0 91.6 (T) 80% K20% SW. 0.2% (NaPO 0.1% Na CO 6.3 75.9 29.9 91.4(U) 80% K-20% SW. 0.2% De ucst 0.2% (Na ale 6 76.6 27.8 92.5

added prior to spray drying 2 actual pigment composition: kaolinite66.8%; satin white 28.6%, TiO 1.7%, oxidized starch 2.9%

" 0.2% Dcqucst 0.2% (NaP0 added to coating formulation after spraydrying actual pigment composition: Kaolinite 77.6%. satin white 19.47:,TiO 1.1%, starch 1.9%

TABLE IV (b) Optical Properties of Coated Sheets after Calendering* Brito drying.

4. The method as claimed in claim 1 wherein the clay is predispersedwith a sufficient amount of alkali metal polyphosphates to disperse theclay in said aqueous suspension.

5. The method as claimed in claim 1 wherein the mixture is predispersedby the addition of an effective amount to disperse the mixture up toabout 1 percent by weight of a mixture of sodium hexametaphosphate andsodium carbonate in a ratio of about 2:] based on the solids in themixture.

6. The method as claimed in claim 1 wherein the mixture is predispersedby the addition of an effective amount to disperse the mixture up toabout 1 percent by weight of a mixture of sodium hexametaphosphate andorganic phosphonate based on the solids in the mixture.

starch sufficient to provide adhesive qualities.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent o- 3854.971 Dated December 17. 1974 Inventor(s) ROBERT F. CONIEY et al.

It is certified that error appears in the aboveidentified patent andthat said Letters Patent are hereby porrected as shown below:

Table II (b) should be inserted after Table II (a) to read:

TABLE II (b) OPTICAL PROPERTIES OF COATED SHEETS AFTER CALENDERING"Gloss Brightness whiteness Opacity Sample 75 @457m Index, 0

Satin White 27. 2 69. 5 30. 8 93.4 Kaolinite Clay 24.1 72.0 28.3 93.3(c) 70% K30% s.w. 25. 0 72.9 25.5 94.9 (D) 70% K30% s. w. fresh 21. 071.2 28.7 93.4

*Two nips at five psig In Table IV (b)-Continued, Sample T should beinserted after Sanple S, to read:

Column 6, Claim 1, line 28, after "corpositions" insert oomprising.

Signed and Scaled this twenty-seventh D y f January 1976 [SEAL] Attest:

RUTH C. MASON c. MARSHALL DANN Arresting Officer Commissioner of Parentsand Trademarks

1. THE METHOD OF PRODUCING AN IMPROVED DRY PARTICULATE COATING PIGMENTCONTAINING SATIN WHITE AND KAOLIN WHICH AFTER DRYING MAY SUBSEQUENTLY BEMADE UP INTO AQUEOUS COATING COMPOSITIONS THE STEPS OF: A. FORMING ASATIN WHITE COMPOSITIONS IN AQUEOUS SUSPENSION; B. ADDING A KAOLINITE TOSAID AQUEOUS SUSPENSION OF SATIN WHITE IN SUFFICIENT AMOUNT O TO RETAINTHE EFFECTIVENESS OF SATIN WHHITE AS A PAPER COATING PIGMENT ONREWETTING AFTER C. REMOVING WATER FROM THE AQUEOUS SUSPENSION TO FORM AFREE FLOWING POWDER.
 2. The method as claimed in claim 1 wherein thekaolinite is added as an aqueous suspension.
 3. The method as claimed inclaim 1 wherein a paper coating adhesive starch is added to saidadmixture prior to drying.
 4. The method as claimed in claim 1 whereinthe clay is predispersed with a sufficient amount of alkali metalpolyphosphates to disperse the clay in said aqueous suspension.
 5. Themethod as claimed in claim 1 wherein the mixture is predispersed by theaddition of an effective amount to disperse the mixture up to about 1percent by weight of a mixture of sodium hexametaphosphate and sodiumcarbonate in a ratio of about 2:1 based on the solids in the mixture. 6.The method as claimed in claim 1 wherein the mixture is predispersed bythe addition of an effective amount to disperse the mixture up to about1 percent by weight of a mixture of sodium hexametaphosphate and organicphosphonate based on the solids in the mixture.
 7. The method as claimedin claim 1 wherein the water is removed by spray drying to a level ofabout 5 percent.
 8. A dry particulate composition suitable forsubsequent formulation in paper coating colors comprising a co-driedmixture of satin white and kaolinite of about 5 percent moisturecontent.
 9. A paper coating composition as claimed in claim 8 havingincorporated therein paper coating adhesive starch sufficient to provideadhesive qualities.